This invention is directed to a coating composition useful for providing a finish on a variety of substrates. In particular, this invention is directed to coatings containing fluorinated organosilane polymers which may be used for finishing the exterior of automobiles and trucks, and which are resistant to soiling and easily cleaned for example by washing with water when soiled.
In order to protect and preserve the aesthetic qualities of the finish on a vehicle, it is generally known to provide a clear (unpigmented or slightly pigmented) topcoat over a colored (pigmented) basecoat, so that the basecoat has an attractive aesthetic appearance, including high gloss and DOI (distinctness of image), and remains unaffected even on prolonged exposure to the environment or weathering. This type of finish is known as a basecoat/topcoat or basecoat/clearcoat finish. It is also generally known that alkoxysilane polymers, due to strong silane bonding when cured, provide finishes with excellent resistance to etching from acid rain and other environmental pollutants, along with good scratch resistance. Exemplary of prior patents disclosing silane polymers for coatings are U.S. Pat. Nos. 4,043,953; 4,518,726 and 4,368,397. Nowadays, these silane coatings are widely used as clearcoats over pigmented basecoats.
However, conventional silane clearcoat finishes still suffer from unsolved problems or deficiencies. In particular, previously disclosed silane coatings have a tendency to soil easily under exterior use conditions. Such soiling not only could seriously and adversely affect long term durability and weatherability of the finish, but also cause the exterior finish of an automobile or truck to lose its luster or other aspects of its attractive aesthetic appearance, including high gloss and excellent DOI, rather quickly in between washings. Given that it is well known that consumers prefer automobiles and trucks with an exterior finish having an attractive aesthetic appearance, rapid soiling of the finish is ever more undesirable.
A number of coatings containing acrylic fluorocarbon polymers have been proposed for use as clearcoats to provide finishes that have high water and oil repellency, stain resistance and good cleanability, for example, as shown in U.S. Pat. Nos. 4,812,337; 5,597,874; 5,605,956; 5,627,238; 5,629,372 and 5,705,276. However, to applicants' knowledge, none of the previously disclosed fluorocarbon finishes employ silane chemistry. Furthermore, there is no suggestion that silane finishes can be made therefrom.
There is a need for a coating composition and in particular an automotive clearcoat that not only is weather- and scratch-resistant, but also that remains relatively dirt free under exterior use conditions and is easily cleaned for example by washing with water when soiled. It is also desirable that such a clearcoat should be capable of being applied using conventional equipment over a variety of basecoats and have excellent adhesion.